The present invention relates to ground water sampling instruments and techniques. More particularly, but not exclusively the invention relates to sampling instruments and techniques for low yield aquifers and perched groundwater zones.
The quality of naturally occurring water is a matter of increasing concern. Various toxic pollutant substances derived from, for example, industrial effluents, human wastes, or natural factors of geological weathering, aging, and erosion often find their way into aquifer systems. Since aquifer systems may involve interconnected bodies of water, it is important to monitor associated groundwater at numerous locations, and because the characteristics of the groundwater usually varies with time, repetitive sampling is usually necessary. While certain characteristics of water can be monitored by detectors placed in a well which provide continuous monitoring, in most instances, more complete data is needed which can more effectively be obtained by the transport of groundwater samples to a full service laboratory.
Prior to obtaining a reliable sample, a well typically must be purged of at least the stagnant water in the well. For many groundwater wells, an operator can travel to a site and both purge the well and collect the necessary sample without delay. However, there are other wells, known as low yield wells, that do not produce a large enough volume of water to satisfy the demand of both purging and sampling without requiring a significant amount of time to accumulate water from the aquifer after being purged. The water that does accumulate in a low yield well stagnates as time passes, further compounding the problems of sample collection. For example, certain low yield wells may never accumulate enough water at any one time to obtain an adequate sample volume. In certain rather extreme situations, a well in a perched aquifer might only produce about 1 liter of water a day when about 4 liters of water are required for a full laboratory sample.
Accordingly, an operator is required to purge low yield wells in one trip and then return to take at least a partial sample after a sufficient time has passed for the accessible well water volume to recover. Depending on the volume of water accessible in the well and the required purging and sampling volumes, this may require multiple and/or extended trips to the well, driving up the time and cost of monitoring the aquifer. Moreover, in the most extreme cases, the water capacity of a single well can be so low that both purging and sampling can each require multiple trips to the well.
Therefore, there is a need for groundwater sampling techniques that reduce the time and effort involved in obtaining individual groundwater samples from perched or low yield aquifers. There is also a need for groundwater sampling techniques that reliably collect and store a sample for later retrieval without disturbing important measurable characteristics of the sample. There is also a need for a device that can automatically collect and hold a groundwater sample without requiring continual operator attendance.
These and other objectives are realized through various embodiments of the present invention.
A novel sample collection apparatus and method are disclosed for automatically collecting a fluid sample from a well.
In one embodiment the present invention provides a method of monitoring groundwater in a low-yield aquifer comprising, providing a pump, at least one water level sensor, and a controller responsive to the at least one sensor for automatically activating the pump; activating the pump when the water level reaches a first threshold as indicated by the at least one sensor; and deactivating the pump when the water level reaches a second lower threshold as indicated by the at least one sensor. The method can also include continuously activating and deactivating the pump until a desired volume of water is provided to a sample container where the sample container is initially substantially devoid of air.
In a second embodiment, an apparatus for collecting a groundwater sample from a low-yield well is provided comprising: a reservoir, a pump for removing water from the low yield well and providing the water to the reservoir; at least one sensor; and a controller for activating and deactivating the pump, the controller activating the pump to fill the reservoir at a flow rate less than about 500 ml/min in response to signals received from the sensor; wherein the controller activates the pump when the water level in the well reaches a first level as indicated by the at least one sensor, and the controller deactivates the pump when the water level in the well reaches a second lower level as indicated by the at least one sensor. The reservoir can be substantially devoid of air and adapted to receive a predetermined volume of groundwater from the pump.
In a third embodiment, an apparatus for collecting a sample from a low-yield well is provided comprising: a pump; a sample reservoir substantially devoid of air for receiving a volume of liquid for subsequent monitoring; a controller for automatically activating the pump to fill the reservoir; at least one fluid level sensor adapted to sense the level of fluid in the well and output at least one signal; wherein the controller sequentially activates and deactivates the pump in response to the at least one signal until the reservoir is filled with a predetermined volume of fluid.
In a further embodiment there is provided an apparatus for collecting a sample from a well comprising a sample reservoir for receiving a volume of liquid for subsequent monitoring; a sample bypass conduit; a pump for removing liquid from the well and providing the liquid to the sample reservoir, a multiway valve having a first position placing the pump in fluid communication with the sample reservoir and a second position placing the pump in fluid communication with the bypass conduit, a controller for automatically activating the pump and the multiway valve, at least one fluid level sensor adapted to sense the level of liquid in the well and output at least one signal, wherein the controller sequentially activates and deactivates the pump in response to the at least one signal until the reservoir is filled with a predetermined volume of liquid.